The present invention relates to fuel injectors, particularly for vehicle internal combustion engines.
In a well-known type of fuel injector, an injection valve is hydraulically opened and closed by the opening and closing of a solenoid actuated control valve. Both valves are subject to highly pressurized fuel from a supply pump or common rail. To reduce engine emissions, fuel systems are being designed for injection at higher and higher pressure. To seal high pressure fuel during closure of the control valve, it is necessary to increase the hold-down force and thereby avoid seat leakage at these higher pressures.
The higher control valve seating force increases the potential for seat damage when debris gets trapped or crushed in the opening and closing control valve. To meet more stringent emissions regulations it has been found that injecting fuel multiple times during one combustion event is required. To achieve fast opening and closing of the fuel injectors, faster opening and closing control valves with less valve lift are being adopted. Control valve lifts under 50 microns are common. Ideally, debris should to be small enough to pass through the valve seat area.
Debris that gets trapped in the seat area will continue to damage that seat as it opens and closes. This significantly reduces the life of the injectors. When damaged, control valve seats no longer seal properly. Fuel delivered by the fuel injector tends to increase when control valve seats leak. This performance change results in unintended fuel delivery increases which can cause engine damage due to over fueling and also rough engine operation due to uneven fuel delivery into the various engine cylinders. As a consequence, the most common reason for replacing fuel injectors is performance problems caused by control valve seat damage.
Techniques are known for addressing this problem to some extent. The fuel from the fuel tank is filtered through multiple filters prior to reaching the fuel injector but some debris gets through these filters. Primary and secondary filters are located between the fuel tank and the entrance to the high pressure fuel pump. At the entrance to the fuel injector a third, small filter functions at the high pressures produced by the high pressure pump. The primary and secondary filters trap about 99% of the debris in the fuel prior to entering the high pressure fuel pump. The remaining debris in the fuel and additional debris from components such as the high pressure pump become trapped in the small filter (typically an edge filter or laser drilled filter).
Filters used to capture debris at the entrance of the injector are challenging to design at a reasonable cost. These filters typically are not serviced over the life of the injector and to avoid plugging, are theoretically designed to allow debris particles smaller than 30 microns to 60 microns in diameter to pass. In general, however, the filter at the entrance to the injector typically will permit particles smaller than about 50 microns to pass. This does not present a plugging problem with respect to the discharge holes for fuel injection, which are typically larger than 100 microns, but does present a problem for the durability of the control valve. Rod-shaped particles that have a diameter under 60 microns but a length of up to 150 to 200 microns can still pass through the entrance filters. These particles cause damage if they pass into the control valve.
Even if the edge region of an entrance edge filter is designed with a 50 micron passage, larger particles are not permanently trapped but, rather, extrude through the passage as rods or flakes with an effective diameter of about 50 microns. Thus, the overall volume of debris reaching the control valve is not reduced by the typical entrance filter. The control valve must hammer the extruded debris down to a size that will pass through the control valve.